Bacterial vaginosis and new partners: why it happens and how to lower the risk

Bacterial vaginosis happens when there is too much of certain bacteria in the vagina and the usual balance tips. According to the CDC (2023) (opens in a new tab), it is the most common vaginal condition in women aged 15 to 44, and the 2025 trial report in the New England Journal of Medicine (opens in a new tab) describes it as affecting about a third of women of reproductive age. It is common, it is treatable, and it says nothing about how clean or careful anyone is.

BV is not classed as a sexually transmitted infection, the NHS (2026) (opens in a new tab) explains, but sex can trigger it or pass it on. The CDC adds that it rarely affects people who have never had sex, and that you cannot get it from toilet seats, bedding or swimming pools. Researchers still do not fully understand what causes it, which is part of why the advice below keeps evolving.

BV matters for more than comfort. Having it raises the risk of getting STIs, including HIV, chlamydia and gonorrhoea, according to the CDC’s 2021 treatment guidelines (opens in a new tab), and in pregnancy it is linked with a higher chance of an early birth. That is why it is worth checking and treating, not ignoring.

The CDC (opens in a new tab) names three things that can upset the normal balance of vaginal bacteria and raise the risk of BV: douching, not using condoms, and having new or multiple sex partners. The NHS (opens in a new tab) lists a change of partner among the things that make it more likely.

The first systematic review of the evidence, a 2008 analysis of 43 studies by Fethers and colleagues (opens in a new tab), found the same pattern in numbers:

Why would a partner matter at all? The 2025 trial report notes evidence that BV-associated bacteria are exchanged between sexual partners, and the CDC’s guidelines note that these bacteria can be found on male genitals. Exactly how sex leads to BV is still not known (CDC). For people in the lifestyle, where new partners are part of the point, this is practical knowledge rather than a reason to worry: BV is common, treatable, and some of the risk is within your control.

Many people with BV notice nothing at all: the NHS (opens in a new tab) says half of women with BV have no symptoms. When there are symptoms, the CDC (opens in a new tab) lists:

• a thin white or grey vaginal discharge;
• a strong fish-like odour, especially after sex;
• pain, itching or burning in the vagina;
• burning when peeing;
• itching around the outside of the vagina.

The NHS adds that BV does not usually cause soreness or itching, and other conditions, including some STIs, can cause similar changes to discharge. That overlap is the reason to get checked rather than guess: a clinician will want to confirm it is BV and rule out an STI.

BV is not caused by poor hygiene, and scrubbing harder does not help. Douching is one of the things the CDC says upsets the vagina’s balance. The NHS (opens in a new tab) suggests a gentler routine that may help prevent BV coming back:

• wash the genital area with water and plain soap, and prefer showers to baths;
• skip perfumed soaps, bubble bath and shower gel in the bath;
• do not use vaginal deodorants, washes or douches;
• do not add antiseptic liquids to the bath or use strong detergents on underwear;
• do not smoke.

A clinician diagnoses BV by examining the vagina and, often, testing a sample of discharge, according to the CDC (opens in a new tab). BV is treated with prescription antibiotics, as tablets, gels or creams. The CDC advises taking the whole course even if symptoms go away, and notes that treatment may also lower the risk of other STIs. In the UK, sexual health clinics treat BV and many offer walk-in appointments (NHS (opens in a new tab)).

BV sometimes clears up on its own, but the CDC recommends being checked and treated if you have symptoms. If you are pregnant, speak to your doctor or midwife about any change in discharge: the NHS notes a small chance of complications, while BV causes no problems in the majority of pregnancies.

BV often returns. The NHS (opens in a new tab) says it commonly comes back, usually within a few months, and a clinician can suggest longer-term options for people who get it often. In a Melbourne study of 139 women treated for BV, Bradshaw and colleagues (2006) (opens in a new tab) found that 58% had it again within 12 months. Past BV, a regular partner throughout the study and female partners were all linked with it coming back, which pointed researchers towards partners.

Nobody can promise that BV will not happen; even the CDC (opens in a new tab) says healthcare providers do not completely understand how to prevent it. Its basic steps are not having sex, limiting partners, not douching, and using condoms the right way every time. For people who choose an active sex life with more than one partner, these are the levers within reach:

• Use condoms correctly, every time, with a fresh condom for each partner. In the Fethers review, condom use was linked with about a fifth lower risk.
• Keep your routine gentle: plain soap and water, no douches, washes or perfumed products (NHS).
• If you share toys, cover them with a fresh condom for each partner (the NHS notes condoms can be used on toys), so fluids are not passed from one partner to the next.
• Notice your own pattern. The NHS says a clinician can help identify triggers, such as sex or your period.
• If BV keeps returning, see a clinician rather than self-treating, and ask about the partner question above.

Our condom size guide covers how to find a condom that fits and which lube is safe with which condom.

BV can spread between female sex partners, the CDC (opens in a new tab) says, and the NHS (opens in a new tab) advises that a partner who is a woman or has a vagina may also need treatment. In the Fethers review (opens in a new tab), having any female partner was linked with about twice the risk of BV, and in the Bradshaw study female partners were linked with BV coming back.

The CDC’s 2021 guidelines (opens in a new tab) note that female partners often both have BV, but that no studies had evaluated treating female partners to stop it returning. If you and a female partner both have symptoms, it is reasonable to be checked together and to tell your clinician about each other.

Because BV is not an STI and not about hygiene, telling a partner can be a short, calm conversation. You might say: “I’ve been treated for BV. It’s a common bacterial imbalance, not an STI, but it can go back and forth between partners, so I wanted you to know. My clinician may ask whether you should be checked or treated too.”

• Tell regular partners, since recurrence is linked with ongoing partners.
• With new partners, condoms from the start lower the risk for both of you.
• Nobody owes anyone details they do not want to share; share what helps the other person decide.
• Health information stays between partners. Never send results to a platform or group chat, including JoinTheSwing.

BV is one part of playing safe. For testing, condoms and the rest of the picture, see our play-safe guide.

1. CDC, December 11, 2023

   About Bacterial Vaginosis (BV)

   BV is an imbalance of vaginal bacteria and the most common vaginal condition in women aged 15 to 44; douching, not using condoms and new or multiple partners raise the risk; the listed symptoms; BV can return after treatment and can spread between female partners; the page states male partners do not need treatment.

2. CDC, 2021 (last reviewed July 22, 2021)

   Sexually Transmitted Infections Treatment Guidelines, 2021: Bacterial Vaginosis

   Risk factors including a new sex partner; BV raises the risk of acquiring STIs including HIV; routine treatment of sex partners not recommended on the evidence then available; no studies of treating female partners.

3. NHS, reviewed June 19, 2026

   Bacterial vaginosis

   Not classed as an STI, but sex can trigger it or pass it on; half of women with BV have no symptoms; it commonly returns within a few months; hygiene advice (plain soap and water, no perfumed products, washes or douches); a partner with a vagina may also need treatment.

4. Vodstrcil et al., New England Journal of Medicine, 2025

   Male-Partner Treatment to Prevent Recurrence of Bacterial Vaginosis

   Open-label randomised trial of 164 couples in monogamous heterosexual relationships in Australia; stopped early; recurrence within 12 weeks 35% (24 of 69) with male-partner treatment vs 63% (43 of 68) without; side effects in treated men were nausea, headache and a metallic taste; describes BV as affecting one third of women of reproductive age.

5. Muzny & Sobel, New England Journal of Medicine editorial, 2025

   Bacterial Vaginosis — Time to Treat Male Partners

   The journal's accompanying editorial on the trial.

6. Fethers et al., Clinical Infectious Diseases, 2008

   Sexual risk factors and bacterial vaginosis: a systematic review and meta-analysis

   43 observational studies: relative risk 1.6 for new or multiple male partners, 2.0 for any female partner, and 0.8 with condom use.

7. Bradshaw et al., Journal of Infectious Diseases, 2006

   High recurrence rates of bacterial vaginosis over the course of 12 months after oral metronidazole therapy and factors associated with recurrence

   139 women in Melbourne treated for BV: 58% had a recurrence within 12 months; past BV, a regular partner and female partners were linked with recurrence.

8. NHS, reviewed January 26, 2024

   Condoms

   Use a new condom every time; condoms can also be used on sex toys; check the use-by date and the CE or UKCA mark; never use two at once; no oil-based lubricant with latex; skip latex with a latex allergy or while using antifungal medicine on the genitals; get help promptly if a condom splits or comes off.